1. Field of the Invention
This invention relates to an improvement on the color exchange and cleaning device of a minibell painting machine which is used for painting vehicles and the like.
2. Description of the Prior Art
Electrostatic painting has been adopted in the process of painting complicated-shaped articles, such as parts of the vehicle.
At the time of practicing electrostatic painting, a high voltage is imposed on the painting machine. Thus, as this voltage exceeds a certain level, atmospheric discharge occurs from conductor elements, such as color valves, existing in a high-voltage sphere in which the painting machine is included. When there appear a lot of atmospheric discharges, the absolute value of electric current flowing when a high voltage is imposed increases with an increase in dark current, thereby tending to cause fire or explosion. To prevent such accidents, a protector incorporated in an electrostatic high voltage generator comes to operation, hence, the electrostatic high voltage frequently exhibits abnormality. When such circumstances are encountered, imposition of the high voltage is terminated to suspend the painting process of the painting machine and consequently an automatic conveyor line for articles to be painted is also stopped. If the painting process is restarted after a temporarily stoppage, color shade or color grain tends to appear on a painted surface to yeild non-conforming articles, and the productivity lowers due to a standstill of a production line.
Atmospheric discharge easily occurs from pointed portions lying in the vicinity of the painting machine with the high voltage imposed thereon, thus, it is necessary to lessen the number of such pointed portions as far as possible.
On the other hand, since a variety of color is used in painting the vehicle and the like, it is necessary each time of exchange of painting color to clean a paint transfer line and the painting machine to prevent occurrence of color mixing. Especially, in case a bell painting machine is employed, careful consideration should be taken because a bell itself is rotating at a great rate.
That is, with the bell rotating at a great rate, as a cleaning medium of high pressure is supplied to the bell and the like, a remaining paint is inconveniently scattered circumferentially due to rotation of the bell, and a large amount of cleaning medium is wasted, this being uneconomical.
Because fo the reasons described above, cleaning is customarily effected separately between two systems: the paint transfer line and the painting machine.
A conventional color exchange and cleaning device for the minibell painting machine is configured as shown in FIG. 3 and comprises two systems or sections. Specifically, a first section or a counter-side color exchange and cleaning section is located in a spot remote from a bell 16 (in a vacant spot adjacent to the automatic painting machine within a booth), and includes color valves 20, 21, 24 and 25, a counter-side manifold 19 provided with a cleaning air valve 23 and a cleaning thinner valve 22, a trigger valve 5 attached to a manifold 30 provided in the vicinity of the bell, a hose 18 connected with the trigger valve 5 and the manifold 19, and a dump valve 7 with a drain hose 8 communicated with the trigger valve 5. A second system or a bell-side color exchange and cleaning section includes a manifold 29 located in the vicinity of the bell and provided with color valves 11 and 12; a low-pressure cleaning air valve 14; and a low-pressure cleaning thinner valve 13, a trigger dump valve 9 provided on the manifold 30, a hose 28 connected with the manifold 29 and the trigger dump valve 9, a hose 4, and a feed tube 17 reaching the bell 16.
In the aforementioned conventional color exchange and cleaning device, since the counter-side color exchange and cleaning section can be cleaned by the use of air and thinner of high pressure, cleaning can be achieved in a short time even if the box is located at a rather remote position. However, in the case of the bell-side color exchange and cleaning section, the bell is an object to be cleaned, thus, it must be cleaned by the use of low-pressure air and thinner.
Therefore, where the hose 28 is long, a long time is necessary for cleaning it, and the flow resistance of the air or thinner flowing through the hose 28 becomes large when the hose is clogged to make it difficult to properly control the pressure of fluid supplied to the bell 16, thereby resulting in the problem of incomplete cleaning.
Consequently, a long time is required for cleaning the bell 16, thereby prolonging the work time of color exchange and degrading the productivity.
In addition, since the bell-side color exchange and cleaning section is located in the vicinity of the bell, the surroundings of the bell become complicated to increase the number of unstable elements causing atmospheric discharge, thereby making the safety questionable.